Hydraulically controllable globe valve

ABSTRACT

A hydraulically controllable globe valve having a stem piston to which pressure can be applied by a spring connected to a pressure source, with the stem piston being able to move from a first end position in the direction of a second end position. Pressure control means are provided which maintain a constant pressure of the hydraulic spring means on the stem piston while the latter moves from the first end position in the direction of the second end position by connecting the hydraulic spring means to a pressure source during a variable portion of the valve lift. The valve can be used, for example, as a gas exchange valve in a reciprocating engine.

FIELD OF THE INVENTION

The present invention relates to a hydraulically controllable globevalve, in particular a gas exchange valve of an internal combustionengine, having a stem piston to which a pressure can be applied byhydraulic spring means connected to a pressure source, and which canmove from one end position in the direction of a second end position.

BACKGROUND INFORMATION

A hydraulic actuator for a globe valve in an internal combustion engine,which is known from German Patent No. 38 36 725, has a piston connectedto the valve shaft and guided in a cylindrical working space, with aspring-loaded arrangement provided at both ends of the piston so thatthe piston is forced, when rest, into a central position in which theglobe valve is partially open. To move the globe valve into an open orclosed position, hydraulic pressure can be alternately applied to thepiston from a pressure source. A feed pump serving as the pressuresource and a switchable multiway valve are provided for this purpose.

A hydraulic valve controller for a globe valve in an internal combustionengine, which is known from German Patent No. 195 01 495, has a helicalcompression spring that loads the globe valve in the closing directionas well as hydraulic spring means that can be connected alternately to apressure source and a pressure sink by a switchable multi-way valve,with these spring means being able to move the globe valve in theopening direction via a stem piston that can move along with the globevalve.

Hydraulic control mechanisms for a gas exchange globe valve in aninternal combustion engine are known from German Patent No. 196 21 951and German Patent No. 196 21 719, in which first spring means loadingthe valve in the closing direction and second spring means loading thevalve in the opening direction via a stem piston are assigned to theglobe valve, with these spring means including a series arrangement ofone mechanical and one hydraulic spring. The second spring means form aspring arrangement with a progressive total spring characteristic, withthe hydraulic spring being prestressed by a force exceeding the maximumforce of the helical spring as a function of the opening work of theglobe valve. A correspondingly high supply pressure for the controlmechanism is provided for this purpose.

A hydraulic control mechanism for a globe valve in an internalcombustion engine, to which there are assigned first spring means forapplying pressure in the closing direction and second hydraulicallycontrollable spring means for applying pressure in the openingdirection, is known from German Patent No. 197 16 042. The secondhydraulically controllable spring means can be cyclically applied withpressure and then relieved again, with an auxiliary control element,which can relieve the pressure on the second hydraulically controllablespring means in the event of a globe valve malfunction, being assignedto these second hydraulically controllable spring means. The auxiliarycontrol element preferably has a 2/2-way valve function and is connectedvia control lines to a pressure supply line and a pressure relief linewhich can be switched by a central actuator having an on-off valve. Theauxiliary control element is also held in its closed rest position by amechanical resetting spring.

As mentioned above, the fact that the actuating energy, e.g., theopening energy, of a exhaust valve fluctuates with the combustionchamber pressure, and thus with the engine load, is a problem in gasexchange valves of internal combustion engines. The conventional remedyis to set different opening forces, which can be done using theabove-mentioned spring means having a series arrangement of onemechanical and one hydraulic spring. One drawback of this arrangement,however, is that the working space volume of the hydraulic springincreases as the opening movement of the valve stem piston begins,causing the hydraulic pressure built up at the spring to drop rapidly.In addition, the hydraulic pressure setting of the hydraulic spring mustbe adjusted to the engine operating state to generate an optimum forcefor opening the valve.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a globe valve of thetype mentioned in the preamble which can be moved by a variableactuating energy supplied by the hydraulic spring means withoutrequiring any variable supply pressures for the hydraulic spring means.

This object is achieved according to the present invention by providingpressure control means which maintain a constant pressure of thehydraulic spring means on the stem piston while the latter moves fromthe first end position in the direction of the second end position byconnecting the hydraulic spring means to the pressure source during avariable portion of the valve lift. This makes it possible to vary theenergy applied to the stem piston during the valve lift by selecting alonger or shorter value for the portion of the valve lift during whichthe hydraulic spring means apply the working pressure of the pressuresource to the stem piston, at the same time maintaining a constanthydraulic spring means pressure. As a result, the actuating energy ofthe globe valve can be varied without changing the working pressure ofthe pressure source.

In one embodiment of the present invention, the hydraulic spring meansare connected to the pressure source by the fact that the pressurecontrol means is provided with a first annular space connected to thepressure source and located in a valve housing surrounding the stempiston as well as a further annular space connected to the hydraulicspring means via a pressure channel, with this second annular spacebeing connected to the first annular space via a control groove in thestem piston during the variable portion of the valve lift. Thisautomatically connects the hydraulic spring means to the pressure sourcewhen the stem piston moves from the first end position in the directionof the second end position, provided that the first annular space isconnected to the pressure source. The hydraulic spring means are alsoautomatically separated from the pressure source as soon as the controlgroove no longer connects the two annular spaces to each other. As longas the two annular spaces are connected via the control groove, theapplication of supply pressure from the pressure source to the hydraulicspring means can be controlled by opening and closing the connectionbetween the first annular space and the pressure source.

In a further embodiment of the present invention, the hydraulic springmeans are connected to the pressure source by providing the pressurecontrol means with a first annular space connected to the pressuresource and located in a valve housing surrounding the stem piston aswell as a control groove, located in the stem piston, which can beconnected to the hydraulic spring means via a pressure channel providedin the stem piston, with the control groove being connected to theannular space during the variable portion of the valve lift. Thisautomatically connects the hydraulic spring means to the pressure sourcewhile the step piston moves from the first end position in the directionof the second end position, provided that the first annular space isconnected to the pressure source. The pressure channel to the hydraulicspring means is arranged in an especially simple and space-saving mannerwithin the stem piston. The hydraulic spring means are disconnected fromthe pressure source as soon as the control groove is no longer connectedto the first annular space. As long as the control groove is connectedto the first annular space, the application of supply pressure from thepressure source to the hydraulic spring means can be controlled byopening and closing the connection between the first annular space andthe pressure source.

In a further embodiment of the present invention, the pressure channelcontains a non-return valve which prevents the pressure in the hydraulicspring means from decreasing via the pressure channel. When the pressurechannel is connected to the pressure source, the non-return valve opensas the pressure in the hydraulic spring means drops below the supplypressure of the pressure source following a movement of the stem piston.

In a further embodiment of the present invention, the first annularspace can be connected to the pressure source via a hydraulic actuatorthat also causes the stem piston to move from a first end position inthe direction of a second end position. This eliminates the need toprovide a separate actuator for the pressure control means. Thebeginning of the variable portion of the valve lift is defined by theconnection between the control groove in the stem piston and the firstannular space. The end of the variable portion of the valve lift isdefined either by separating the control groove from the first annularspace or switching the hydraulic actuator.

In a further embodiment of the present invention, the pressure controlmeans for connecting the hydraulic spring means to the pressure sourcehave a shutoff element for closing the pressure channel, with theshutoff element being alternately connected to the pressure source and apressure sink through hydraulic means for opening and closing thepressure channel at a first end and being held open during the variableportion of the valve lift. The shutoff element can be controlledindependently of the pressure in the pressure channel through hydraulicmeans. Using the shutoff element eliminates the need for a hydraulicmedium flowing to the hydraulic spring means to pass through an on-offvalve with an adequately large opening cross-section.

In a further embodiment of the present invention, the shutoff elementfor closing the pressure channel is assigned a resetting spring thatoperates in the closing direction of the shutoff element, and theshutoff element is connected to the hydraulic spring means in a way thatallows pressure to be applied, opening the pressure channel against theforce of the resetting spring. This allows the shutoff element to openand close as a function of the difference between the pressure in thehydraulic spring means and the control line pressure.

In a further embodiment of the present invention, the control line canbe connected to the pressure source and the pressure sink via ahydraulic actuator that also triggers the movement of the stem pistonfrom the first end position in the direction of the second end position.The hydraulic actuator thus controls both the stem piston and theshutoff element. In an alternative embodiment of the present invention,the control line is connected to the pressure source via a throttle andto the pressure sink via an on-off valve. The control line is preferablycoupled with the pressure source and pressure sink so that the shutoffelement also opens when the stem piston moves from its first endposition, in which the valve is closed, in the opening direction.

In a further embodiment of the present invention, the pressure controlmeans define the variable portion of the valve lift, and thus the valveactuating energy, as a function of a counter-pressure acting upon thevalve, in particular as a function of the combustion chamber pressureand thus the engine load in the case of a gas exchange valve of aninternal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic longitudinal sectional view of a firstembodiment of a hydraulically controllable globe valve in an internalcombustion engine having a stem piston to which a pressure can beapplied as well as pressure control means that can be connected to apressure source via a control groove in the stem piston.

FIG. 2 shows a view according to FIG. 1, but for a second embodiment ofthe hydraulically controllable globe valve having pressure control meansthat are completely integrated into the stem piston.

FIG. 3 shows a view according to FIG. 1, but for a third embodiment ofthe hydraulically controllable globe valve having pressure control meansdesigned as a shutoff element for a closable pressure channel.

FIG. 4 shows a view according to FIG. 1, but for a fourth embodiment ofthe hydraulically controllable globe valve having a hydraulic actuatorand a throttle as the pressure control means.

DETAILED DESCRIPTION

An internal combustion engine, in particular a reciprocating engine fora motor vehicle, has multiple working cylinders in the known mannerwhose combustion chambers are each provided with at least one globevalve 1 for supplying combustion air (intake valve) and for dischargingthe combustion exhaust gases (exhaust valve). A hydraulic controlmechanism 30, 40, 50, 60, which can be designed in different embodimentsaccording to FIGS. 1 through 4, is provided to control each globe valve1. Hydraulic control mechanisms 30, 40, 50, 60 of globe valves 1 of allworking cylinders in the internal combustion engine preferably can becontrolled by engine electronics designed in the form of a centralcontrol unit. Each of FIGS. 1 through 4 shows the valve in its closedposition.

According to all embodiments of the hydraulic control mechanism, globevalve 1 has a valve stem 2 and a spring holder 3 permanently connectedto the latter. A spring force operating in the valve closing directioncan be applied to valve stem 2 by a helical compression spring 4 viaspring holder 3.

Valve stem 2 is positioned in corresponding hydraulic control mechanism30, 40, 50, 60 so that it can move linearly together with a stem piston5, with stem piston 5 guided in a cylindrical guide 6 a of a valvehousing 6. At one point, cylindrical guide 6 a widens to form a workingspace 7, through which stem piston 5 passes. Working space 7 contains acontrol piston 8, which forms one piece with stem piston 5. Controlpiston 8 includes an upper and a lower plunger 8 a and 8 b, which entercorresponding pressure chambers 7 a and 7 b of working space 7. Pressurechambers 7 a and 7 b are designed so that they are separated from theremaining volume of working space 7 by plungers 8 a and 8 b at the endpositions of stem piston 5.

In reference to FIG. 1, a first embodiment of the globe valve accordingto the present invention having hydraulic control mechanism 30 isdescribed below. In this control mechanism 30, a working space 9, intowhich one end of stem piston 5 enters, is provided in valve housing 6 atthe end of stem piston 5 facing away from helical compression spring 4.Working space 9 and a pressure cylinder 10 which are connected to eachother by a line 11, form a hydraulic spring means that is connected inseries to a mechanical spring means in the form of a compression spring12. Spring arrangements of this type are already known from GermanPatent No. 196 21 951 and German Patent No. 197 16 042 cited above anddescribed in detail in these publications.

In the illustrated first position (rest position) of stem piston 5,working space 9 is connected to a supply line 16 via a channel 13 and agroove 14 in stem piston 5 as well as via an annular groove 15 providedin the housing. The working pressure of hydraulic control mechanism 30generated by a pressure source (not illustrated) is present in supplyline 16, and the hydraulic medium can flow into control mechanism 30 viathis supply line 16. With stem piston 5 in its rest position, themaximum working pressure is therefore present in hydraulic spring means9, 10, 11, so that a maximum compressive force is exerted on an upperend 5 a of stem piston 5 in the opening direction of globe valve 1. Atthe same time, upper pressure chamber 7 a is connected to a control line20 via a groove 18 in stem piston 5 and an annular space 19 in thehousing, with this control line 20 being relieved of pressure via asuitably switched control valve 31. Working space 7 is permanentlyconnected to the pressure source via a supply line 17 so that, whilestem piston 5 is in this position, a force is exerted on control piston8 in the valve closing direction, with this force, combined with theforce of helical compression spring 4, being sufficient to hold stempiston 5 and globe valve 1 in the rest position against the force ofprestressed hydraulic spring means 9, 10, 11.

The switchover of control valve 31 causes stem piston 5 to move out ofits rest position, connecting control line 20 to supply line 21 and thusplacing upper pressure chamber 7 a under the working pressure. Thecompressive forces acting upon stem piston end 5 a and upper plunger 8 aovercome the compressive forces acting upon lower plunger 8 b as well asthe spring forces of helical compression spring 4, so that stem piston 5moves together with globe valve 1 from the illustrated rest position inthe direction of the globe valve opening position.

As stem piston 5 withdraws, groove 14 leaves annular space 15, thusdisconnecting hydraulic spring means 9, 10, 11 from supply line 16. Asstem piston 5 continues to withdraw, the pressure in hydraulic springmeans 9, 10, 11 therefore threatens to drop, reducing the force on stempiston 5. To avoid this pressure loss, valve housing 6 contains pressurecontrol means 22 to 25 to variably connect hydraulic spring means 9, 10,11 to the pressure source. Pressure control means 22 to 25 include apressure channel 22, which can be closed off by a non-return valve,between working space 9 and an annular space 24. A control groove 25 isalso provided in stem piston 5 and connects annular space 24 to annularspace 19, and thus to control line 20, when stem piston 5 is in thecorrect position.

When stem piston 5 thus moves out of its first end position (restposition), the connection between groove 14 and annular space 15 isfirst established and, simultaneously or immediately afterward, aconnection is established between annular spaces 19 and 24 via controlgroove 25. The working pressure present in control line 20 reachespressure channel 22 through the connection between the two annularspaces 19 and 24 and opens non-return valve 23 against the force of aspring of non-return valve 22 and against the pressure in working space9 so that the working pressure remains applied to hydraulic spring means9, 10, 11. To end this state, either control line 20 is relieved ofpressure by resetting control valve 31 to the position shown in FIG. 1,or by interrupting the connection between annular space 24 and controlgroove 25 by withdrawing stem piston 5. In both situations, the refluxof the hydraulic medium to working space 9 ends, and non-return valve 23once again closes off pressure channel 22. During the portion of thevalve lift in which both annular spaces 19 and 24 are connected viacontrol groove 25, hydraulic spring means 9, 10, 11 can be connected tothe pressure source or a pressure sink by control valve 31 in a largelyselectable manner. This makes it possible to compensate the pressuredrop in hydraulic springs 9, 10, 11 caused by stem piston 5 leavingworking space 9, or even prevent it from happening in the first place.

At the end of the valve lift, stem piston 5 reaches its second endposition in which lower plunger 8 b enters lower pressure chamber 7 b,and this pressure chamber is connected via a groove 26 and an annularspace 27 to control line 20, which is now relieved of pressure by theprevious switchover of control valve 31. At the same time, groove 14connects to an annular space 28, which is permanently connected to thepressure sink via a pressure relief line 29, when stem piston 5 is inthis second end position. Consequently, hydraulic spring means 9, 10, 11is also relived of pressure when stem piston 5 is in this position,allowing globe valve and stem piston 5 to return to the first endposition.

Hydraulic control mechanism 30 according to the present invention canpreferably be used to control the exhaust valves of the internalcombustion engine mentioned in the preamble which can open only withhigh gas pressures in the combustion chambers. With different loads onthe engine, gas pressures of different levels and different lengths arepresent in the combustion chambers, exerting forces on globe valve 1 inits closing direction and making it difficult to open the valve.Hydraulic control mechanism 30 for opening the globe valve musttherefore not only be able to overcome the maximum possible forcesexerted in the valve closing direction but also provide, during theglobe valve period, an adequate actuating energy, which, moreover,should not last too long. As described above, this condition is achievedby connecting hydraulic spring means 9, 10, 11 to the pressure source ofcontrol mechanism 30 during a variable portion of the valve lift. Indoing this, the working pressure of the pressure source is adjusted tothe maximum necessary force application, while the period or distance ofthe valve lift over which the high working pressure is applied to thehydraulic spring means can be defined as a function of the energyrequired while globe valve 1 opens, i.e., in particular as a function ofengine load. In the present embodiment, the beginning of the variableportion of the valve lift is defined by annular spaces 19 and 24 beingconnected via control groove 25, while the end of the variable portionof the valve lift is defined by pressure channel 22 being relieved ofpressure after control valve 31 returns to the position shown in FIG. 1or, at the latest, when annular space 24 and control groove 25 aredisconnected from each other.

In a modified embodiment of hydraulic control mechanism 30, pressurecontrol means 22 to 25 are replaced by a pressure channel betweenworking space 9 and the pressure source which can be shut off by anadditional on-off valve, in particular a 2/3-way valve.

FIG. 2 shows a second embodiment 40 of the hydraulic control mechanismaccording to the present invention in which pressure channel 22illustrated in FIG. 1, together with corresponding annular space 24 invalve housing 6, is replaced by a pressure channel 32 provided in stempiston 5. Pressure channel 32 is connected via connecting bores 33 to acontrol groove 34, which travels over annular space 19 connected tocontrol line 20 when stem piston 5 is withdrawn. A non-return valve 35,which corresponds to non-return valve 23 in FIG. 1, is provided betweencontrol groove 34 and groove 14 in pressure channel 32.

Hydraulic control mechanism 40 illustrated in FIG. 2 operates in muchthe same way as control mechanism 30 in FIG. 1. The switchover of acontrol valve 31 designed as a 3/2-way valve applies the workingpressure from the pressure source (not illustrated) to control line 20,and hydraulic spring means 9, 10, 11, which is also under pressure,moves stem piston 5 from its first end position (rest position) in thedirection of a second end position (open position). This interrupts theconnection between groove 14 and annular space 15, at the same timeclosing the connection between control groove 34 and annular space 19.This ensures that the working pressure remains applied to working space9 via pressure channel 32 and channel 13 while non-return valve 35 isopen, as long as control line 20 is connected to the pressure source andcontrol groove 34 has not crossed annular space 19.

FIG. 3 shows a modified embodiment of a globe valve 1 according to thepresent invention, compared to the embodiments illustrated in FIGS. 1and 2, having a hydraulic control mechanism 50. Like in the otherembodiments, globe valve 1 is assigned a helical compression spring 4which acts upon valve stem 2 via a spring holder 3 and exerts a force inthe closing direction of globe valve 1. A stem piston 5, to which isassigned a control piston 8 guided in a working space 7, is provided ina cylindrical guide 6 a of a valve housing 6 to actuate globe valve 1.Plungers 8 a and 8 b, which enter pressure chambers 7 a and 7 b, therebyseparating a pressure chamber from working space 7 in the valve endpositions, are provided at both ends of control piston 8.

A compressive force, which is capable of moving stem piston 5, togetherwith globe valve 1, against the force of helical compression spring 4and the other forces acting upon globe valve 1, can be applied to upperend 5 a of stem piston 5 by a hydraulic spring means 9, 10, 11 in theopening direction of globe valve 1. Hydraulic control mechanism 50 canbe switched via a control valve 31 designed as a 3/2-way valve thatconnects control line 41 to either a pressure source (not illustrated)via a supply line 42 or a pressure sink (not illustrated) via a pressurerelief line 43. Control line 41 opens into working space 7, which isconnected to a further control line 44. Control line 44 provideshydraulic control of a shutoff element 46 of a pressure channel 48.Pressure channel 48 connects working space 9 to the pressure source viaannular space 14 and supply line 42 and can be closed off by shutoffelement 46. Shutoff element 46 is designed as a stopper which is pressedinto a conical seat 47 by a compression spring 45 and by the controlline pressure. The pressure in working space 9 can be applied to stopper46 in the opening direction.

The function of hydraulic control mechanism 50 can be described asfollows. When globe valve 1 is in its first end position (restposition), as shown in FIG. 3, the maximum working pressure is appliedto both working space 7 and hydraulic spring means 9, 10, 11. Becauseupper pressure chamber 7 a is relieved of pressure, the combined forceson control piston 8 and the force on helical compression spring 4 aresufficient to hold globe valve 1 in the illustrated rest positionagainst the compressive force of hydraulic spring means 9, 10, 11. Theswitchover of control valve 31 allows control line 41 to be connected topressure relief line 43, thereby relieving working space 7 of pressure.This causes stem piston 5 to move from the illustrated end position inthe direction of a second end position (open position), in which globevalve 1 is open. At the same time, the switchover of control valve 31relieves control line 44 of pressure, so that the pressure in workingspace 9 presses stopper 46 against compression spring 45, openingpressure channel 48. Open pressure channel 48 connects the hydraulicspring means to supply line 42 and thus to the pressure source.

As stem piston 5 moves in the direction of the second end position,groove 14 separates from annular space 15, while working space 9 remainsconnected to the pressure source via pressure channel 48 and annularspace 15. As soon as plunger 8 a has left corresponding pressure chamber7 a, and annular space 19 is no longer connected to groove 18, theswitching position of control valve 31 no longer affects the movement ofstem piston 5, since the forces acting on control piston 8 cancel eachother out. As a result, control valve 31 can be switched back to theillustrated position at any point in the movement of the stem pistonfrom its first end position to its second end position or, with globevalve 1 in any position, between its closed rest position and its openposition.

This again applies pressure to working space 7 and control line 14 sothat stopper 46 is pressed back into its seat 47, thereby interruptingthe connection between hydraulic spring means 9, 10, 11 and the pressuresource.

As stem piston 5 continues to withdraw, the pressure in hydraulic springmeans 9, 10, 11 decreases according to the increase in volume. With stempiston 5 in its second end position, groove 14 connects to annular space19, which completely relieves hydraulic spring means 9, 10, 11 ofpressure. Prior to this pressure relief, control valve 31 must return tothe position shown in FIG. 3, so that the working pressure in workingspace 7 acting upon control piston 8 from above can hold stem piston 5in its second end position against the force of helical compressionspring 4 while pressure chamber 7 b separated by lower plunger 8 b issimultaneously relieved of pressure.

A further switchover of control valve 31 and a corresponding pressurerelief in working space 7 cause the stem piston to return to theillustrated first position, which, however, has no effect on stopper 46,due to the pressure relief in working space 9. The stopper is also heldin its closing position by compression spring 45.

In hydraulic control mechanism 50 according to FIG. 3, the operatingprinciple described above allows the pressure in hydraulic spring means9, 10, 11 to be maintained at the maximum working pressure of thecontrol mechanism during a portion of the valve lift that can be variedin time or space. The variable portion of the valve lift begins when theswitchover of control valve 31 causes stem piston 5 to start moving, andit ends at a freely selectable time when control valve 31 is reversed.

Stopper 46 also provides a safety function if the pressure source fails,causing the working pressure in control mechanism 50 to drop. If thehydraulic spring means is not completely relieved of pressure in thiscase, stopper 46 is automatically opened by the pressure differencebetween working space 9 and pressure channel 48, thus reducing thepressure in working space 9. However, since the force of compressionspring 45 prevents the pressure in working space 9 from dropping all theway to the level of the remaining working pressure, an additionalnon-return valve can be provided between annular space 15 and workingspace 9 in channel 13, thus allowing hydraulic medium to flow out ofworking space 9 into annular space 15, but preventing it from flowingback in.

FIG. 4 shows a fourth embodiment of the globe valve according to thepresent invention having a corresponding hydraulic control mechanism 60.Hydraulic control mechanism 60 largely corresponds to control mechanism50 illustrated in FIG. 3, with 3/2-way valve 31 provided in FIG. 3 andserving as a control valve being replaced by a 2/2-way valve 51 inconjunction with a throttle 52 in a bypass line 53. Bypass line 53connects control line 41 to supply line 42.

The switchover of 2/2-way valve 51 serving as the control valve movesstem piston 5 from the illustrated first end position in the directionof the second end position, which quickly relieves working space 7 ofpressure via pressure relief line 43. Even before significant quantitiesof hydraulic medium can flow from supply line 42 to control line 41 viathrottle 52, upper plunger 8 a emerges from pressure chamber 7 a, afterwhich control valve 51 can immediately return to the illustrated initialposition.

As in the case of control mechanism 50 shown in FIG. 3, stopper 46 isopened by the pressure in working space 9 when control line 44 isrelieved of pressure, and working space 9 is connected to the pressuresource via pressure channel 48. The working pressure that builds back upover time in working space 7, and thus in control line 44, causesstopper 46 to close gradually during the valve lift. The behavior ofstopper 46 is largely influenced by the dimensioning of throttle 52,which means that an adjustable throttle 52 can vary the closing speed ofstopper 46, for example as a function of the operating conditions of aninternal combustion engine equipped with the globe valve according tothe present invention.

According to the proposed arrangement, the working pressure can beapplied to hydraulic spring means 9, 10, 11 for different lengths oftime during a variable portion of the valve lift, allowing the openingenergy exerted on globe valve 1 to be varied accordingly. Shutoffelement 46 is advantageously positioned so that it can be adjusted witha small volume of hydraulic medium, at the same time connecting apressure channel with a comparatively large flow cross-section. Apressure channel with a large flow cross-section makes it possible tosignificantly increase the opening power of the control mechanism.

A shutoff element 46, like the one provided in control mechanisms 50 and60 according to FIGS. 3 and 4, can, of course, also be controlledthrough other means. In particular, control line 44 can contain anelement for inverting the pressure in the control line, thus openingstopper 46 when the working pressure is present in control line 44 andclosing it when control line 44 is relieved of pressure.

What is claimed is:
 1. A hydraulically controllable globe valve,comprising: a stem piston capable of being moved from a first endposition in a direction of a second end position; a hydraulic springarrangement connected to a pressure source and for applying a pressureto the stem piston the hydraulic spring arrangement includes amechanical biasing element; and a pressure control arrangement formaintaining constant the pressure applied by the hydraulic springarrangement on the stem piston while the stem piston moves from thefirst end position in the direction of the second end position byconnecting the hydraulic spring arrangement to the pressure sourceduring a variable portion of a valve lift operation.
 2. The globe valveaccording to claim 1, wherein the globe valve corresponds to a gasexchange valve of an internal combustion engine.
 3. The globe valveaccording to claim 1, wherein the pressure control arrangement variablydefines a portion of the valve lift operation during which the pressurecontrol arrangement maintains constant the pressure on the hydraulicspring arrangement as a function of a counter-pressure acting upon theglobe valve.
 4. The globe valve according to claim 1, furthercomprising: a valve housing surrounding the stem piston, wherein: thestem piston includes a control groove and a pressure channel, thepressure control arrangement includes, in order to connect the hydraulicspring arrangement to the pressure source, a first annular spaceprovided in the valve housing and capable of being connected to thepressure source, the control groove is capable of being connected to thehydraulic spring arrangement via the pressure channel, and the controlgroove is connected to the first annular space during the variableportion of the valve lift operation.
 5. A hydraulically controllableglobe valve, comprising: a stem piston capable of being moved from afirst end position in a direction of a second end position; a hydraulicspring arrangement connected to a pressure source and for applying apressure to the stem piston; a pressure control arrangement formaintaining constant the pressure applied by the hydraulic springarrangement on the stem piston while the stem piston moves from thefirst end position in the direction of the second end position byconnecting the hydraulic spring arrangement to the pressure sourceduring a variable portion of a valve lift operation; a valve housingsurrounding the stem piston; and a pressure channel, wherein: the stempiston includes a control groove, the pressure control arrangementincludes, in order to connect the hydraulic spring arrangement to thepressure source: a first annular space provided in the valve housing andcapable of being connected to the pressure source, and a further annularspace capable of being connected to the hydraulic spring arrangement viathe pressure channel, and the further annular space is connected to thefirst annular space via the control groove during the variable portionof the valve lift operation.
 6. The globe valve according to claim 5,further comprising: a hydraulic actuator for simultaneously triggering amovement of the stem piston from the first end position in the directionof the second end position, wherein the first annular space is capableof being connected to the pressure source via the hydraulic actuator. 7.The globe valve according to claim 5, further comprising: a non-returnvalve for preventing the pressure from decreasing in the hydraulicspring arrangement via the pressure channel, the non-return valve beingarranged in the pressure channel.